A few other possible explanations…1) Scripture says that angels “in heaven” see the Beatific Vision. Maybe there are angels that have never been in heaven?
2) I remember reading somewhere that as different/advanced as a human is to an animal, or as an animal is to a plant…this is how advanced each of the 9 choirs of angels are to each other. So, it’s possible that some angels are ALWAYS in heaven (ie Seraphim/Cherubim) and some are NEVER there (until judgement day, because their job is to serve the world/humanity).
An example of the latter, is I’ve heard that the angels here on earth did not know that Our Lady was to give birth to Christ until it happened. Those angels who “brought tidings of great joy” to the Shepherds on Christmas we’re either angels from heaven or were earthly angels who had to be told, themselves, from heaven, of the news.